Flying on Friday? Brace for another round of winter-weather disruptions.

Airlines were already canceling flights for Friday ahead of a winter storm that's forecast to dump up to a foot of snow across the Midwest, including in Chicago and its busy air-travel hubs. Most big carriers also were waiving rebooking fees for fliers ticketed through Chicago and at airports across the Great Lakes region.

Nationwide, more than 735 flights have already been canceled, flight-tracking service FlightAware showed as of 7:20 p.m. ET on Thursday. The bulk of those came at Chicago's two major airports: O'Hare is a hub for both American and United while Midway is one of the busiest bases for Southwest.

Southwest and American were the first to start paring their Midwest schedules because of the storm.

Southwest told USA TODAY's Today in the Sky blog that "due to the operational limitations created by the storm system,"  it would suspend flights at Midway airport from 8 p.m. local time on Thursday through "at least" noon local time on Friday.

Airlines in recent years have begun canceling flights in advance of big storms. That allows carriers to keep their planes, crews and passengers from getting "stuck" at snowbound airports. It also enables a quick re-start of operations when the weather clears.

"Proactive cancellations allow our customers either more time to reschedule their travel plans or the ability to reroute their trip, utilizing other connection points in our network to complete their travel," Southwest said about its preemptive cancellations in the Midwest.

The carrier said it would monitor the storm and make adjustments as needed.

Southwest said it also would allow affected Midwest and Great Lakes customers to make one change to their itineraries without paying a fare difference. Southwest is the lone major carrier not to charge change fees, which can cost $200 and up at other U.S. airlines. But passengers flying on U.S. carriers still typically also pay a recalculated fare when making a flight change. Southwest said waiving that procedure would free up fliers to move travel to avoid the storm.

Other airlines had also begun to cancel flights, FlightAware's data showed.

Among those was American, which had preemptively canceled at least 140 combined mainline and regional flights for Friday, according to FlightAware.

American also was allowing affected customers to make changes without paying change fees or recalculated fares.

United, Delta, JetBlue and Air Canada were among other big carriers waiving rebooking charges for customers in the U.S. Midwest and in the Great Lakes region. Details varied by airline, but they generally allowed fliers to make one change to their itineraries without paying change fees or recalculated fares. Airports covered also varied by carrier, but covered a spread of destinations from Iowa and Minnesota east through western New York state and Ontario.